1. Field of the Invention
The present invention relates to the field of integrated circuit (IC) manufacturing, and more specifically, to a method of and an apparatus for using plane waves to control critical dimension (CD) for photolithography.
2. Discussion of Related Art
An IC device, such as a microprocessor, may be fabricated on a substrate, such as a wafer. The wafer may include many layers that have been formed by adding or removing material. The material may include semi-conducting material, such as silicon, or insulating material, such as silicon oxide, or conducting material, such as copper. Some processes that may be used to add material to the wafer may include chemical vapor deposition (CVD), sputtering, electroplating, oxidation, and ion implantation. Other processes that may be used to remove material, partly or completely, from the wafer may include wet etching, dry etching, and chemical-mechanical polishing (CMP).
Photolithography may be used in conjunction with certain processes to limit processing to a pattern of features on the wafer. A thin film of a light-sensitive material, such as a photoresist, is first coated on the wafer. A mask is used at each layer to define the pattern of features. The mask is aligned to the wafer in an imaging tool, such as a stepper or a scanner. The imaging tool couples light from a source with projection optics to expose a latent image in the photoresist. Dose is the amount of light energy that is delivered per unit area. Then, a developer solution selectively removes the photoresist to form a pattern that is a function of the portions that have been exposed. Subsequently, a dry or wet etchant may replicate the pattern printed in the photoresist into the material on the wafer.
The yield of the microprocessor fabricated on the wafer may depend on CD of the features in the pattern. When the CD of the feature is about the same size as the wavelength of the exposure light, diffraction of the exposure light will degrade the CD.
Thus, a need exists for a method of improving control of CD and an apparatus for improved control of CD.